1. Field of the Invention
This invention relates to the preparation of low viscosity polyester polyols which are liquid at room temperature and to the use of these polyols in the preparation of hydrolysis-resistant, noncellular or cellular polyurethane and/or polyurethane-polyurea molded articles, particularly shoe soles, having improved mechanical properties.
This invention further relates to using a polyoxytetramethylene glycol or a mixture of polyoxyalkylene glycols having a molecular weight or average molecular weight of from about 162 to 600 as an initial component for the polycondensation of polyesters and processing the polyester into molded articles.
2. Description of the Related Art
The preparation of elastic, noncellular or cellular isocyanate addition polymer molded articles, defined as polyurethane molded articles, or polyurethanepolyurea molded articles, using the isocyanate addition polymerization process with the help of low pressure- or high pressure technology is well known from numerous patent and literature publications.
U.S. Pat. No. 3,099,516, (DE AS No. 11 96 864) discloses a method of forming elastic, as well as rigid, polyurethanes, as well as all modifications lying there between. The process includes foaming compounds possessing hydroxyl groups together with polyisocyanates in the presence of blowing agents and catalysts. The extent of rigidity or elasticity of the resulting polyurethane is governed by the selection of the suitable polyesters possessing hydroxyl groups, polyethers, polyether esters, polyester amides, or other hydroxyl containing material, and reacting this with the desired organic polyisocyanate. Chain extending agents, such as diamines or glycols, may also be used.
The preparation of optionally cellular polyurethane elastomers using polyester polyols as higher molecular weight polyhydroxyl compounds is likewise known to those skilled in the art.
For example, optionally cellular polyurethane elastomers are prepared using a low pressure process according to EP A No. 00 17 060 through reactions of organic polyisocyanates, polyester polyols obtained through polycondensation of organic dicarboxylic acids with a 1,4-butanediol-, 1,5-pentanediol-, 1,6-hexanediol-mixture and chain extending agents.
U.S. Pat. No. 4,218,543 (DE A No. 26 951) discloses the preparation of optionally cellular, elastic molded articles, which have a dense surface layer, from polyurethane-polyurea elastomers using the high pressure process. The process includes forming the polyurethane-polyurea elastomers by the reaction of organic polyisocyanates and polyhydroxyl compounds, such as polyester polyols and aromatic di- and/or polyamines which are optionally substituted by alkyl groups in the ortho position relative to the amino groups. The elastomer so formed is then subjected to a one-shot reaction molding technique to form the molded article.
Among the disadvantages in the processing of polyester polyols and isocyanates into polyurethane polymer molded articles using low pressure and high pressure processes are the higher melting points of the polyester polyols, of about 50.degree. C. and higher, and their higher viscosities compared to polyether polyols, thereby requiring higher processing temperatures. Polyester polyols also generally possess poor miscibility with other starting components. Another disadvantage is the limited hydrolysis stability of the polyurethane and polyurethane-polyurea elastomers prepared when using polyester polyols as polyhydroxyl compounds.